Plating apparatus and method

ABSTRACT

The present invention comprises a metal plating apparatus and method, particularly suitable for autocatalytic (i.e., electroless) plating, comprising a pressurized sealable vessel for disposing a substrate to be plated and for the circulation of plating solutions wherein temperatures and pressure are highly controllable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing of U.S. ProvisionalPatent Application Ser. No. 60/541,687, entitled “PressurizedAutocatalytic Vessel and Vacuum Chuck”, filed Feb. 4, 2004. Thisapplication is also related to U.S. patent application Ser. No.10/778,647, entitled “Apparatus and Method for Highly ControlledElectrodeposition”, filed Feb. 12, 2004, which claims priority of U.S.Provisional Patent Application Ser. No. 60/447,175, entitled“Electrochemical Devices and Processes”, filed Feb.12, 2003, and whichis a continuation-in-part application of U.S. patent application Ser.No. 10/728,636, entitled “Coated and Magnetic Particles and ApplicationsThereof”, filed Dec.5, 2003, which claims priority of U.S. ProvisionalPatent Application Ser. No. 60/431,315, entitled “Solid Core SolderParticles for Printable Solder Paste”, filed on Dec. 5, 2002, and thespecifications and claims thereof are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to the plating of substrates via metaldeposition. Such plating involves either electrolytic plating orelectroless plating, otherwise commonly referred to as autocatalyticplating.

2. Background Art

During a typical autocatalytic plating process, catalytically inducedchemical reactions cause the continuous deposition of a metal onto asolid surface. Autocatalytic plating reactions are driven primarily bythe temperature of the reaction, and secondarily by the solution pH andthe relative concentrations of the metal complexes and theircorresponding reducing agents. Typically, the substrate surface isprepared for electroless deposition by making it cathodic relative tothe metal species to be deposited to create a continuous surface layerof initiation sites for the redox reactions.

Note that the following discussion refers to a number of publicationsand references. Discussion of such publications herein is given for morecomplete background of the scientific principles and is not to beconstrued as an admission that such publications are prior art forpatentability determination purposes.

Electroless plating has been used for electronic assembly components.There is now a significant interest in using it for plating siliconwafers and other wafer scale and semi-conductor devices. However, it isdifficult to control spurious and extraneous metal deposition ontosurface areas where the metal is not desired. Because autocatalyticplating is governed by the chemical activity of the surface exposed tothe plating solution as well as by the chemical activity of the platingsolution, metal often deposits wherever and whenever a suitablyactivated surface and a plating solution of sufficient chemical activitycome in contact.

Deposit edge resolution is not a primary concern with regard to largecoverage areas, but it is of greater concern with regard to the platingof semiconductor wafers and substrates at micron feature line widths. Atmicron and submicron feature sizes, the magnitude of plating resolutionand definition errors can approach, and even exceed, the featureseparation distance. This can cause conductor bridging and electricalshorting of the wafer or substrate.

In conventional practice, the propensity for electroless platingchemical solutions to deposit metal indiscriminately is controlled byincorporating any number of chemical rate inhibitors. The inhibitorsraise the chemical activation threshold for the reduction of the metalions out of solution thereby limiting their deposition to only wellactivated surfaces. However, the addition of inhibitors can negativelyimpact the utility of plating for subsequent joining/connectingprocedures. For example, a residue of incorporated organics on, orwithin, the plating deposit can preclude solder wetting or wire bondingto that metal surface. This effect has discouraged the wide use ofconventional electroless plating technology for wafer scale electronicjoining applications.

Electroless plating is conventionally done in an open vessel or tank.The vessel is typically made of either plastic or of plastic lined metalto prevent the electroless chemicals from spontaneously depositing outof solution when the plating solution comes in contact with a metalsurface.

A plastic, glass or polytetrafluoroethylene (“PTFE”) coated immersionheater is typically used to maintain the bath at the optimal processtemperature, which may range from 35 to 85 degrees Celsius. The bath istypically mixed by stirring or by pumping the solution in the tank.

The substrate is typically prepared by first immersing it in a chemicalcleaning solution followed by a rinse and an immersion in a catalyticactivator solution. The activated substrate is then immersed in the hotplating bath until the desired thickness of the plating layer is builtup. The item is then removed, rinsed again, and dried.

The following example outlines a typical process flow for conventionalelectroless plating as it is conventionally practiced in multiple tanksfor an Electroless Nickel Immersion Gold (“ENIG”) process:

-   -   1. immersion in an aluminum cleaner;    -   2. immersion in a zincate activation solution;    -   3. immersion in a desmut or strip solution;    -   4. immersion in a second zincate solution;    -   5. rinse in deionized water;    -   6. immersion in a heated nickel electroless plating bath        solution;    -   7. multiple rinses (1-3 times) in deionized water;    -   8. immersion in an immersion gold bath solution; and    -   9. rinse in deionized water.

This process is conventionally practiced in a serial arrangement of opentanks, with the wafers or substrates fixed in a plastic or plasticcoated rack or wafer carrier. The wafers or substrates are manuallymoved in their carrier from tank to tank or are conveyed by a mechanicaltransporter. The requirement to physically move the wafer or substratefrom tank to tank creates a significant risk of damage to the wafer. Therisk of damage is increased by the ongoing trend in the semiconductorprocessing industry to “thin” wafers by chemical or mechanical means,making an already delicate structure even more fragile.

To function well, conventional electroless plating deposition processesrequire an optimum bath volume to plated work surface area loadingratio. Therefore, a serial bath, open tank electroless plating line,once constructed, will function well only within a fairly narrow rangeof work volumes and area ratios.

Therefore, there is a need to better adapt autocatalytic platingtechniques and processes for optimal application in the semiconductorindustry.

With respect to the electrolytic plating of thin wafers such as thosefound in the semiconductor industry, the existing electrolytic platingmethodology suffers from certain limitations. To plate a wafer, thewafer is typically fixed onto a rigid substrate to allow for plating,and an array of metallic contacts are electrically connected via a wireto a direct current power supply and to a counter-electrode (i.e. theanode). The metallic surfaces of contacts must be completely isolated sothat deposits are not allowed to build up around the contact. Suchbuild-up detrimentally fuses the contact point to the surface of thewafer and at the completion of the process can result in a tearing orremoval of the deposited film at the contact point.

Another limitation of electrolytic plating is that the resulting surfacearea of the exposed contact can greatly affect the amperage densityapplied and the cathode efficiency of the wafer, which must be strictlycontrolled. This causes inaccurate or inconsistent results in the meantarget thickness of the deposited film. Also, the contacts are a sourceof impurities that can be introduced onto the wafer.

Electrolytic plating requires that a radial array of contacts bedisposed around the periphery of the wafer to be plated. A current isbussed in through the wafer's edge where the array is disposed. Thehigher the number of contact points around the periphery of the wafer,the better the distribution of current. The existing designs forelectrolytic plating require a chemical contact point and thereforecreate limitations in the number of contact points that can be suppliedaround the periphery and effectively sealed to prevent a detrimentalinfluence on the surface area of the plated wafer.

A limitation of copper electro-deposition on silicone wafers is that thecopper electrolyte and the resulting copper deposit can contaminate thesilicon. This converts the semiconductor material into a conductivematerial, thereby ruining the entire wafer by converting the surfacefrom insulator to conductor.

Currently, the semiconductor industry favors the “damascene” process fordepositing copper, and techniques for depositing the copper patternshave progressively favored the electrolytic deposition of the metal. Anumber of clamping or sealing mechanisms have been devised to seal offthe edges and back side of the wafer thereby exposing, through acircular or other patterned window, the surface to be plated. Suchdevices are fairly complicated in that typically a sandwich comprising aback plate, an O-ring seal, and a top frame must be clamped, bolted, orfixed to the wafer. This limits the effectiveness of automating thewafer handling process in a production environment.

Consequently, the complicated nature of such devices limits thecross-sectional area of the bussing elements which connect to thecontact points. The resulting buss cross-section is reduced to favor themechanical design, which detrimentally affects impacity or currentcarrying capacity. This causes the requirement for a higher voltage tocomplete the current flow through the fixture.

A better, more effective method or apparatus for holding a substrateduring plating and for sealing portions of the substrate and electricalcontacts is required.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a plating apparatus comprising apressurized, sealable vessel within which to dispose a substrate duringplating of the substrate, a controllable source of a plating fluidlinked to the vessel, a holding apparatus to secure the substrate withinthe vessel until the plating of the substrate is complete, and at leastone opening through which plating fluids pass in and out of the vessel.In the preferred embodiment, the apparatus is particularly applicable toautocatalytic plating.

The invention is particularly suitable to plating semiconductor wafers.

The apparatus preferably comprises a closed loop system between thecontrollable source of plating fluid and the vessel. The inventionpreferably comprises a pressure control system to control isostaticpressure within the vessel. The controllable source of plating fluidspreferably comprises a system for the discreet, sequential introductionand removal of fluids into and from the vessel and preferably comprisesa plurality of nozzles and conduits. The at least one opening in thevessel preferably comprises a port.

The apparatus preferably comprises a temperature control system, thesystem preferably controlling a temperature to within approximately ±1°C. The temperature control system preferably heats and cools the platingfluid at a rate faster than approximately 0.5° C. per second, morepreferably at a rate faster than approximately 1.0° C. per second, andmost preferably at a rate faster than approximately 2.5° C. per second.The temperature control system may be disposed outside of the vessel toaffect a temperature of a fluid prior to it entering the vessel and/ordisposed over the vessel and/or disposed in the vessel. The temperaturecontrol system may also be disposed in at least one wall of the vessel.

The vessel preferably comprises a volume of less than less thanapproximately 5 liters, more preferably less than approximately 3liters, still more preferably less than approximately 2 liters, stillmore preferably less than less than approximately 1 liter, and mostpreferably less than approximately 0.5 liter.

The apparatus preferably comprises a baffle system disposed within thevessel. The apparatus preferably comprises a cathode disposed in thevessel to receive an electric current into the vessel.

The vessel preferably comprises a base plate and a cover to dispose onthe base plate. The holding apparatus preferably comprises a vacuumchuck which preferably a base and at least one vacuum cavity in thebase. The apparatus preferably comprises at least one membrane disposedover the cavity(ies). The membrane preferably comprises a membrane thatis deformable in response to a vacuum, and preferably comprises anelastomeric membrane.

The vacuum chuck preferably comprises a center shuttle disposed in thebase. The vacuum chuck also preferably comprises an edge seal bootdisposed on the base, and the edge seal boot preferably comprises anedge skirt to contact the substrate and seal a portion of the substrate.The apparatus may comprise an electric bridge contact disposed in theedge skirt, and the contact preferably comprises an array of contacts.

The present invention also comprises a method for depositing metal on asubstrate comprising providing a pressurized, sealable vessel, securingthe substrate within the sealable vessel, introducing at least oneplating fluid into the vessel, removing the plating fluid(s) from thevessel, and removing the substrate from the vessel after the metal hasbeen deposited on the substrate.

The method also preferably comprises introducing the fluids discreetlyand sequentially, and removing the fluids discreetly and sequentially.

The method preferably comprises controlling an isostatic pressure withinthe vessel. The method may also comprise disposing a cathode in thevessel and sending an electrical current to the cathode.

The method preferably comprises controlling a temperature of fluid(s),preferably to within approximately ±1° C. The method also preferablycomprises heating and cooling the plating fluid preferably at a ratefaster than approximately 0.5° C. per second, more preferably at a ratefaster than approximately 1.0° C. per second, and most preferably at arate faster than approximately 2.5° C. per second. The temperature ofthe fluid(s) is affected before introducing it into the vessel or whileinside the vessel.

The method also preferably comprises providing a baffle system andaffecting the flow of the fluid(s) within the vessel using the bafflesystem.

The method preferably comprises providing a holding apparatus anddisposing the holding apparatus in the vessel, wherein the holdingapparatus secures the substrate within the vessel. The holding apparatuspreferably comprises a vacuum chuck comprising at least one vacuumcavity. The method preferably comprises disposing a deformable membraneon the cavity(ies) and disposing the substrate on the membrane. Vacuumis preferably applied to secure the substrate to the vacuum chuck.

Preferably, a boot comprising an edge skirt is provided and the boot isdisposed on the vacuum chuck. An electrical bridge contact may bedisposed in the boot and an electrical current is sent through thebridge contact.

A primary object of the present invention is to provide for the platingof a substrate while keeping the substrate in position throughout theentire plating process.

Another object of the invention is to provide for better control ofautocatalytic plating processes, particularly with respect to smallsubstrates.

A primary advantage of the present invention is the ability to finelycontrol the plating processes with regard to, but not limited to,initiation rates, deposition rates, temperature control, and pressurecontrol.

Another advantage of the present invention is the ability to reduce thevolumes required for plating.

Another advantage of the present invention is the ability to minimizethe risks of damage in plating small, expensive substrates and thusreduce the costs inherent in such damage.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention are set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated into, and form a partof, the specification, illustrate one or more embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating one or more preferred embodiments of the invention and arenot to be construed as limiting the invention. In the drawings:

FIG. 1 is a perspective view of the preferred embodiment of the vesselof the present invention;

FIG. 2 is a cross-sectional view of the embodiment of FIG. 1.

FIG. 3 is a cross-sectional view of the preferred embodiment showing theapplication of vacuum into the vessel;

FIG. 4 is a cross-sectional view of the preferred embodiment showing theintroduction of a plating solution;

FIG. 5 is a cross-sectional view of the preferred embodiment showing thecirculation of a plating solution;

FIG. 6 is a cross-sectional view of the preferred embodiment showing thepurging of a plating solution;

FIG. 7 is a cross-sectional view of the preferred embodiment showing arinsing process;

FIG. 8 is a perspective view of the preferred embodiment showingmultiple solution nozzles;

FIG. 9 is a cross-sectional view of the preferred embodiment of thevacuum chuck;

FIG. 10 is a perspective view of the preferred embodiment of the vacuumchuck;

FIG. 11 is a cross-sectional view of the preferred embodiment of thevacuum chuck showing the initial application of vacuum;

FIG. 12 is a cross-sectional view of the preferred embodiment of thevacuum chuck showing the subsequent application of vacuum;

FIG. 13 is a cross-sectional view of the preferred embodiment of thevacuum chuck showing the release of vacuum through the center shuttle;

FIG. 14 is a cross-sectional view of the preferred embodiment of thevacuum chuck showing the release of vacuum through the center shuttle;

FIG. 15 is cross-sectional view of the edge skirt of the preferredembodiment;

FIG. 16 is a cross-sectional view of the seal created by the edge skirtof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention comprises a metalplating (i.e., metal deposition) apparatus and method. The apparatuscomprises a vessel or other enclosure to contain a substrate to beplated while the substrate is subjected to one or more plating processesand/or materials and fluids. Such processes include the electrolytic andelectroless (i.e., autocatalytic) deposition of metal(s). As usedherein, “substrate” is defined as any object comprising a surface ontowhich metal deposition is to occur, including, but not limited to, asemiconductor wafer. The present invention provides for the plating of asubstrate in a single vessel without the need to transfer the substrateto other vessels for exposure to other plating fluids or process steps.As used herein, a “plating fluid” is any fluid to which a substrate isexposed during a plating process including, but not limited to, chemicalsolutions, rinsing solutions, and metal solutions. In the preferredembodiment, the apparatus also comprises a controllable source of aplating fluid. Such a controllable source preferably comprises anysource and delivery system known in the art including, but not limitedto, containers such as tanks or other vessels linked to conduits for thetransfer of fluids wherein the delivery may be controlled by any numberof systems such as, for example, temperature control systems, pressurecontrol systems, pumps, valves, etc., or manual control.

In the preferred embodiment, the apparatus further comprises a chuck,preferably a vacuum chuck, to hold the substrate in a desired positionduring the process(es). In the preferred embodiment, the apparatus andmethod are particularly suited for use in the semiconductor industry,but may be utilized wherever the indiscriminate deposition of metal ontosurface areas must be avoided and/or where a greater level of controlover the deposition of the metal is desired such as for theautocatalytic deposition of ceramic substrates or other types ofelectronic substrates. Although the apparatus and method of the presentinvention may be utilized for both electrolytic and autocatalyticplating, the remainder of this description focuses on autocatalyticplating.

As depicted in FIG. 1, the preferred embodiment of the present inventioncomprises sealed plating vessel 20 within which an item/substrate to beplated, such as substrate 100 (depicted in the figures as a wafer),remains during the entire plating process. Vessel 20 is preferablyhydrostatically sealable. The plating fluids to which substrate 100 isexposed are preferably introduced discreetly (i.e., so that the unwantedcontamination of one fluid with another does not occur) into the cell,thereby allowing for the sequential introduction of fluids at theappropriate process step. The present invention, therefore, preferablyprovides for a closed loop system between the source of the platingfluids and the vessel 20.

Although the plating of one substrate 100 is described herein and isrepresentative of the preferred embodiment, other embodiments of vessel20 permit the plating of a plurality of substrates, preferably fixed ina tight arrangement to increase the total throughput.

Vessel 20 preferably comprises a cover such as dome 22 which ispreferably disposed over a bottom portion such as base plate 24. Anyshape or configuration for vessel 20 may be utilized in accordance withthe present invention, although a domed structure with a circular baseis preferred. Laminar flow formation is preferably promoted by utilizinga non-rectangular shape of cell 30 adjacent to solution inlet 26. Baseplate 24 is preferably machined and preferably comprises stainlesssteel, plastic, or other rigid material. Dome 22 preferably comprisessupply port 26, which in the preferred embodiment is preferably annular,for the introduction of fluids into vessel 20. Dome 22 also preferablycomprises return port 28 for the return flow of fluids out of vessel 20.Although a dome, base plate, and ports are described herein, anystructure or means known in the art to provide for a sealable vessel andto provide access therein for the introduction and expelling of fluidsmay be utilized.

In the preferred embodiment, heating and cooling controls describedbelow are provided. Such control of temperature is more effective if themass of vessel 20 is reduced. Therefore, in the preferred embodiment,certain dimensions including, but not limited to, wall thickness areminimized in manners well-known in the art to provide for greatertemperature control.

FIG. 2 shows a cross-section of the preferred embodiment of vessel 20.As dome 22 is fitted over base plate 24, enclosed cell 30 is formedwithin vessel 20. Coupling nozzle 36 is preferably disposed on supplyport 26 and return port 28 to connect fluid supply conduit 50 to supplyport 26 and to connect fluid return conduit 52 to port 28. Fluid supplyconduit 50 transfers solution 200 (which may comprise any fluid to beintroduced into vessel 20, such as, but not limited to, chemical platingsolutions) from solution tank 54 and into cell 30, preferably throughthe use of pump 56. Fluid return conduit 52 returns solution 200 to tank54. Preferably, a flow and pressure control system, preferablycomprising valve 60, pressure regulator 62, and filter 64, is disposedalong fluid return conduit 52.

Baffle system 88, as shown in FIG. 2a, is preferably disposed withincell 30 (securing means not shown) to improve the flow quality of fluidswithin cell 30. As plating fluid 200 passes about and/or through bafflesystem 88, a pressure of the fluid, within cell 30, as described below,is distributed and improves laminar flow. Any design for baffle system88 known in the art to control the flow of fluids may be utilized.

Seal 34 is preferably provided, although any means known in the art forensuring the containment of fluids and gases within cell 30 may beutilized. Drain basin 38 is preferably disposed under base plate 24 tocollect fluids when dome 22 is separated from base plate 24. Releasedfluids are preferably collected through drain return cup 68 and sent viadrain conduit 70 to storage (not shown) or to tank 72. Filter 74 may bedisposed on drain conduit 70.

Vessel 20 preferably comprises an apparatus for holding the object to beplated (e.g., substrate 100) in a fixed or other desired position duringthe plating process. The apparatus preferably comprises chuck 40, and inthe preferred embodiment, comprises a vacuum chuck. The overall designof chuck 40 is preferably circular, but any geometric shape may beutilized. In the preferred embodiment, chuck 40 comprises a base that inthe preferred embodiment comprises base plate 24 (although chuck 40 cancomprise a separate, dedicated base) which in turn preferably comprisesvacuum chamber 44 and vacuum cavities 46, 46′. Vacuum cavities 46, 46′may number one or more, although two are depicted in the figures.

Chuck 40 also preferably comprises diaphragm 42 which is disposed over,and completely seals, vacuum cavities 46, 46′. Notwithstanding thenumber of vacuum cavities depicted throughout the figures, one or moresuch cavities may be utilized. Membrane 42 preferably comprises adeformable sealing material, such as a flexible or elastomeric membranethat can deform in response to vacuum and that preferably comprises amaterial that is chemically non-reactive and temperature resistant, suchas, but not limited to, thin rubber silicone. In a method of the presentinvention, substrate 100 is disposed on diaphragm 42.

Vacuum port 48 is connected to a vacuum source system (not shown). FIG.3 shows how in the preferred embodiment, as vacuum is applied intovacuum chamber 44 through vacuum port 48, vacuum chamber 44, and vacuumcavities 46, 46′, diaphragm 42 is distorted so that vacuum void 47 formsbetween diaphragm 42 and substrate 100. The vacuum within vacuum void 47holds substrate 100 against base plate 24 and seals the contact surfacesbetween substrate 100 and diaphragm 42. Vacuum cavities 46, 46′preferably comprise a series of concentric rings or grooves that aresized to create a footprint pattern smaller than the main diameter ofsubstrate 100. Thus, the back side of substrate 100 is protected fromexposure to catalysts or other chemicals.

FIG. 4 shows the introduction of electroless chemical solution 200 whichpreferably flows through port 26 into cell 30 preferably until cell 30is filled to the desired level. Return port 28 is preferably provided topermit the return or cycling of solution 200 back to its source, such astank 54. FIG. 5 schematically shows an embodiment of the presentinvention which provides for a continuous circulation of solution 200through cell 30. The duration of the flow of solution 200 through cell30 and the residence time for a given portion of solution 200 withincell 30 is determined by the process flow and the desired amount ofexposure to each solution.

In the preferred embodiment of the present invention, return conduit 52,through which solution 200 is returned to its source, is linked to apressure system preferably comprising elements such as valve 60 andpressure regulator 62. By regulating the back pressure with valve 60,isostatic pressure may be introduced and/or maintained within cell 30and can act upon the surface of substrate 100 at the reaction interface.During plating, the pressure within cell 30 is preferably maintainedabove atmospheric pressure.

As noted, typical electroless plating processes suffer from the spuriousdeposition of metal in areas where deposition is not desired and must beinhibited to maintain an acceptable level of process control. Modulatingthe hydrostatic pressure of the plating solution surrounding thesubstrate being plated can control the electroless plating depositionrate. Specifically, increasing the hydrostatic pressure in a closedspace that holds both the plating fluids and the substrate to be platedwill reduce the plating rate and increase the threshold for platinginitiation in direct proportion to the overpressure. This approach, inpart, involves the suppression of hydrogen gas generation at theboundary layer between the metal surface and the plating fluid. Theplating rate can be retarded by increasing the direct application ofhydrostatic pressure to the system at up to several bars ofoverpressure. At pressures greater than one atmosphere, the platingreaction can be suspended so that there is no net metal deposition ontothe substrate.

Therefore, this preferred application of isostatic back pressure in thepresent invention provides an additional kinetic property or additionalkinetic control that provides for better process control without theneed to add organic inhibiters. The kinetic control provided by thepresent invention permits the use of autocatalytic gold and otherautocatalytic pressure chemical formulations which have previouslyproven too reactive and too difficult to control, as they require a highlevel of organic inhibiters that typically result in an undesirablemetallurgical structure/material.

Through the application of hydrostatic pressure, the present inventioncomprises the precise control of both the initiation and rate of platingby directly controlling the physical environment of the item to beplated. Other examples of the better control offered by the presentinvention, discussed more fully below, are the control over temperatureand the electrical activation of various surfaces to provide a morerefined control over the deposition process. Such control isparticularly valuable within the semiconductor industry because the linefeature associated with semiconductor patterns is too small to permit ahigh incidence of organic material co-deposits. Such co-deposits reducethe metallurgical density of the resulting metal pattern. By controllingthe environment as with the present invention, the requirement toincorporate complexing agents, stabilizers, inhibitors, etc. is largely,if not completely, obviated. The present invention, therefore, providesfor a metal deposit that is free of the co-deposited and incorporatedorganic species commonly found in the metal deposits resulting fromconventional electroless plating.

The pressure of the solution in cell 30 is regulated by pressure valve38 or other type of pressure regulator, which preferably pressurizes thecell to one or two atmospheres above open cell, or ambient, pressure.However, any pressure may be utilized. For example, valve 38 introducesback pressure into cell 30, which optionally is monitored and controlledby pressure gauge 62 or other controller. The ability to pressurize cell30 provides control over pressure dependent characteristics of theplating process, for example deposit kinetics, which results in improvedperformance and an improved deposit.

Controlling the pressure in cell 30 also improves solution exchange andion supply on all surfaces of substrate 100, including deep filled viasand planer surface areas. Thus, submicron structures can be successfullyplated and nanoscale vias can be filled uniformly.

With regard to electrolytic plating, pressurizing cell 30 alsosuppresses the formation of gases such as hydrogen at the depositioninterface, (i.e. the cathode, or substrate, surface). These gases causeundesirable porosity or voids resulting in micropittings that typicallyoccur in a deposit on the surface of the cathode. Gases such as hydrogenalso may reduce the mechanical strength of the deposit; if hydrogen isleft in the boundary area, brittle deposits or highly stressed depositsmay be formed, resulting in tensile failure and possibly resulting inthe deposit peeling back from substrate 100. The integrity of the bondof the deposit, such as a metallic interconnect, to substrate 100 iscritical to assure the high reliability necessary for electroniccomponents.

For applications in the submicron range, particulates, pores, andmicropittings that would normally be acceptable in traditional platingapplications are not tolerable because of the small size of the featuresto be plated as well as the required thinness of the deposit. Thus, theoverall control of micropittings is of paramount importance ifsemiconductor wafers are to be electroplated. By using pressurization tominimize gas formation, the integrity of the initial deposit on thesurface of substrate 100 (when the voltage or the potential is at itshighest), which creates the first boundary layer between substrate 100and the metal being deposited, will be greatly improved. This results ina surface morphology of sufficient quality to successfully platesubmicron structures.

Also, the ability to raise the pressure in cell 30 allows for the use oftemperatures higher than used conventionally such as, for example,temperatures higher than the typical 85° C.

As shown in FIG. 6, after the desired processing is complete, dome 22can be lifted to create evacuation port 80. Evacuation port 80preferably comprises the open area encircling base plate 24 and dome 22as they are separated, thereby providing for the a complete purging ofsolution 200. All purged fluids, including solution 200, are preferablycollected in basin 38. FIG. 6 shows catch basin 38 which is disposedover one or more of return cup 68 (such as return cups 68, 68′, 68″,68′″, 68″″, 68′″″ as shown in FIG. 8).

As shown in FIG. 7, after the purging of solution 200, another couplingnozzle 36′, which is connected via conduit 156 to rinsing source 154(containing rinsing fluid 158 such as, but not limited to, deionizedwater), and is preferably connected to port 26 and/or port 28 to injectrinsing fluid 158 into cell 30 to completely rinse out solution 200 andto purge rinse water 158. Vessel 20 can be in an open or a closedposition during this step.

The injection and purging of water can be repeated a number of times asdescribed. Subsequent solutions are preferably applied sequentially byattaching several coupling nozzles such as coupling nozzles 36, 36′,36″, 36′″ shown in FIG. 8. All of the steps can be repeated for any ofeach subsequent exposure to a solution. Thus, solutions may be appliedwithout contaminating one with another, and they may be applied in acontrolled time fashion to provide for accuracy in the process and tobuild the desired metal deposit film onto substrates.

To apply fluids sequentially, nozzle turret system 136 or other similar(to accomplish the same task)is preferably utilized in one embodiment,as shown in FIG. 8, which can, for example, rotate to sequentiallydispose distinct nozzles on vessel 20. By multiplying the number oftanks, the number of nozzles and the number of return cups, an unlimitednumber of process steps can be applied to the vessel to provide asophisticated process control capability without transferring substrate100 or other substrates from vessel to vessel. The present inventionalso allows for the pressurization of the work zone with an inert gas,such as nitrogen, to control or eliminate oxidation on the metalsbetween process steps (i.e., elimination of exposure to oxygen).

An example of the method of the present invention applied to an ENIGplating deposition comparable to the conventional electroless platingprocess sequence described in the background section above is asfollows:

-   -   1. filling the cell with an aluminum cleaner;    -   2. rinsing the cell with deionized water;    -   3. filling the cell with a zincate solution;    -   4. rinsing the cell with deionized water;    -   5. introducing a nickel electroless plating bath solution to the        cell and heating the cell to operating temperature;    -   6. rinsing the cell with deionized water;    -   7. introducing an immersion gold bath solution to the cell and        heating the cell to operating temperature; and    -   8. rinsing the cell with deionized water.

In the present invention, plating solution 200 can be held outsidevessel 20 at a temperature just below the minimum plating temperatureand quickly raised to the optimum operating temperature just as platingsolution 200 is introduced into cell 30. Plating solution 200 can beheated either by heating tank 54, by passing it through thermostaticallycontrolled heating coil 58 (shown in FIG. 2) or by embedding a heatingsystem directly within the walls of vessel 20, such as, for example,incorporating a heating/cooling jacket 59 adjacent walls 32 of dome 22as shown in FIG. 2 a. The heating system can comprise a heating/coolingjacket through which a thermal control fluid such as, but not limitedto, water and/or glycol can be circulated. Other thermally conductivematerials that may be utilized in such a heating system include gases.Also, a combination of electrically resistive heating and gaseouscooling, thermoelectric heating and cooling, and combinations thereofmay be utilized. In effect, any heating/cooling system known in the artmay be used to regulate temperature. Also, a temperature control systemmay be combined with such a heating system, thermocouples or othersystems may be included to provide feedback to the temperature controlsystem to keep plating solution 200 within a desired temperature withinapproximately ±1° C.

In addition to maintaining a constant temperature, the present inventionprovides for the ability to quickly heat and/or cool a plating fluid.Such cooling and heating rates are preferably at rates of greater thanapproximately 2° C. per second, more preferably at rates of greater thanapproximately 1° C. per second, and most preferably at rates of greaterthan approximately 0.5° C. per second.

The temperature regulating feature of the present invention isparticularly helpful given that electroless plating processes are highlydependent upon solution temperatures. Most autocatalytic platingchemical solutions are designed to operate within a very narrow range oftemperature to achieve their catalytic effect and can heat in situ.

The present invention provides for better and more efficient processmanagement in part because the volume of the cell can be much smallersuch as approximately 1-5 liters (but can be much smaller such as 0.5liters or smaller) in comparison to the tank facilities utilized inconventional plating processes. The relatively smaller volume of platingsolution 200 in use at any one time facilitates a higher degree ofthermal management and plating rate control than can be afforded by theopen tank electroless plating methodology. The smaller size isespecially suited when using a “static” plating embodiment describedbelow wherein fluid is not circulated within vessel 20 while depositionis taking place.

Another benefit of the reduced volume is that, because the amount of theorganic chemicals in the solution is reduced, the resultingmetallurgical quality of the deposited film is higher. For example, theuse of autocatalytic gold allows thicker deposit features that exceed 7micrometers, thereby allowing an electroless, post forming tool to formcolumns in precious metals such as gold and platinum.

Although the figures and the preferred embodiment describe hereindescribe an apparatus and method wherein plating fluids are moved into,within, and out of vessel 20, another embodiment provides that platingfluids may be introduced into vessel 20 and held statically (i.e., notcirculated within vessel 20). In this “static fluid”, non-flowembodiment, plating reactions occur between the static chemicalsolutions and the surface of substrate 100. The initiation and rate ofplating is controlled by temperature control and/or hydrostaticoverpressure control. Operating the plating process in this static fluidmode provides for rigorous control of the volume of plating fluid 200.In other words, the amount of chemical used per substrate 100 can betitered to the point of use, and it is not necessary to hold the entirethe source of plating solution 200 at operating temperatures. The volumeof plating fluid 200 can be heated at either the point of use (i.e.,within vessel 20) or immediately preceding the introduction of platingfluid 200 in to vessel 20. Therefore, the activity and performance ofplating chemicals is preserved even as the amount of chemicals expendedper substrate during the plating process is conserved. This embodimentis particularly suitable when the dimensions of vessel 20 are greatlyreduced in volume and/or in terms of such dimensions as wall thickness,etc.

In the preferred embodiment, vessel 20 comprises electrode 76, whichpreferably comprises a ring-shaped cathode. Electrode 76 is disposedwithin vessel 20 (connection not shown) and can be electrically biasedto walls 32 or substrate 100. Electrode 76 can be employed toelectrically activate the substrate to be plated to initiate the platingprocess. Electrode 76 can also be used to prevent plating depositionfrom going out of solution and onto vessel 20.

Electrode 76 is connected to direct current voltage power supply 78.Base plate 24 and dome 22, which are preferably manufactured of a metalthat can be utilized as an electrode, such as, but not limited to,stainless steel or titanium, comprise the counter-electrode (i.e.,anode). This provides a voltage potential on the surface of base plate24 and dome 22, protecting them from metal deposition. The use of baseplate 24 and dome 22 as an anode can also provide a control scheme toaccelerate the initiation of the electroless process, which is typicallycontrolled by bath loading. The control scheme “fine tunes” the controlover the plating process. Initiation can be controlled by increasing ordecreasing the voltage into cell 30.

In accordance with the present invention, the polarity and amplitude ofbias voltage of ring electrodes can be varied to facilitate anodicprotection of the cell elements exposed to the plating solution duringthe process (conventional electroless plating processes can controlplating initiation only by adjusting levels of plating bath additivesand bath temperature). The cell design has a resident cathode electrodewhich can be used to compensate dynamically for variations in theexposed wafer surface area to be plated (conventional electrolessplating processes have a fundamental limitation as to the platingsurface load which can be plated at any given time which places limitson the flexibility of the conventional electroless plating linehardware).

As detailed, the preferred embodiment of the vacuum chuck is shown inFIGS. 9-16. Vacuum chuck 140 preferably comprises center articulatingshuttle 180 for interfacing substrate 100 with automated end effectors(e.g., Y-shaped effector 220) and robotics for wafer handling and waferautomation. Vacuum chuck 140 is preferably rotatable, which providesadvantages in uniformity of deposit. Center articulating shuttle 180 ispreferably disposed within base plate 124. As shown in FIG. 11, whensubstrate 100 is positioned on chuck 140, center articulating shuttle180 holds substrate 100 above base plate 124 to expose an outerperimeter of the back side of substrate 100. Substrate 100 can then becarried from the back side such as, for example, by effector 220 asshown in FIG. 10. Fastener 118 holds diaphragm 142 to base plate 124 sothat only that portion of diaphragm 142 disposed on center articulatingshuttle 180 rises above base plate 124. Thus, handling can be interfacedwith conventional robotics.

FIG. 11 show substrate 100 held to center articulating shuttle 180 asvacuum is applied through port 186 into vacuum chamber 182 and vacuumcavities 184, 184′ (any number of cavities may be provided). The vacuumcauses diaphragm 142 to deform, thereby creating corresponding voids188, 188′. FIG. 12 shows center articulating shuttle 180 lowered intoposition so that substrate 100 is set onto backing plate 124. FIG. 12shows the application of vacuum through port 148 into vacuum chamber 144and cavities 146, 146′, 146″ (any number of cavities may be provided).This causes diaphragm 142 to deform and create corresponding voids 147,147′, 147″ so that substrate 100 is held onto, and sealed against,backing plate 124. FIG. 14 shows shuttle 180 retracted further uponrelease of vacuum in chamber 182 so that it does not interfere with therotation, if such is desired, of substrate 100.

In the preferred embodiment, edge seal boot 190 is disposed at theperiphery of diaphragm 142. Edge seal boot 190 comprises any flexiblematerial that may provide a seal. Edge seal boot 190 may be utilized inconjunction with any type vacuum chuck such as, but not limited to,vacuum chuck 40 described in FIGS. 1-7, although it is depicted hereinin relation to chuck 140. As detailed in FIG. 15, edge seal boot 190 isconstructed so that it provides for vacuum chamber 144 to extend aboveand around the periphery of substrate 100, preferably when centershuttle 180 is in a position prior to bringing substrate 100 into fullcontact with base plate 124. Edge seal boot 190 preferably comprisesedge skirt 192 which collapses upon the application of vacuum withinvacuum chamber 144. As shown in FIG. 16, upon the application of vacuumthrough port 148, edge seal boot 190 preferably collapses. The design ofthe wall thickness of edge bladder 190 is preferably in a staged fashionso that a controlled collapse of edge seal boot 190 pulls edge skirt 192into contact with the surface of substrate 100, creating an effectiveair and gas seal on the surface of substrate 100. Because a hydrostaticseal is created which protects the edges and backside of substrate 100from contact with plating chemicals, there is no need for masking orcoating the backside of the wafer.

With respect to electrolytic plating, an electrolytic contact withsubstrate 100 is not required but is preferably incorporated byproviding electrical bridge contact 196 and electrical buss ring 194 asshown in FIG. 15. In practice, substrate 100 is placed concentricallywithin electrical buss ring 194 which has a diameter greater than themain diameter of substrate 100 so that substrate 100 can nest withinelectrical buss ring 194. The surface of ring 194 is exposed to the topside and is approximately flush with the surface of substrate 100.

Electrical bridge contact 196 is preferably embedded in edge seal boot190, and preferably comprises an evenly distributed array of contacts,preferably so that electrical bridge contact 196 is isolated when edgeseal boot 190 is not under vacuum. When vacuum is applied and edge skirt192 is pulled into contact with substrate 100, electrical bridge contact196 contacts ring 194 to cause an electrical contact to the surface ofsubstrate 100. This results in a continuity from a, preferably directcurrent, power supply, thereby bussing current in a 360 degreemulti-point contact along the periphery of substrate 100.

Edge skirt 192 also provides a seal to prevent contamination of the backside and the periphery are of substrate 100 from the copper electrolytesolution and also to isolate electrical contacts 196 from exposure tothe electrolyte thereby preventing deposits from forming on electricalbridge contact 196. This provides for an easier and less damagingremoval of substrate 100 upon completion of electrolytic plating. Thisalso reduces the maintenance required for electrical bridge contact 196which would typically suffer from a build-up of deposits.

The bussing circuitry described above can be used in a notic and ketoticfashion and with pulse and periodic reverse regimes. Electrolyticplating processes benefit from the use of the described array ofelectrical bridge contact 196. The result is a lower resistance bussingof the current from buss ring 194 to the surface of substrate 100thereby requiring a lower voltage and providing preferential conditionsfor the electro deposition process.

Chuck 140 can be utilized in open and closed electroplating cells, in avertical or horizontal position, and can be affixed to a bearing device(not shown) and rotationally actuated so that the leading edge effectsdue to electrodeposition from a flowing electrolyte are mitigated byrotating substrate 100 continuously through the electrodepositionprocess to facilitate a homogeneous deposit thickness on the wafer.

Because plating processes typically occur at the final stage of waferprocessing, a considerable investment in materials and work has alreadybeen made to a wafer before plating, and any damage to a wafer duringplating results in a substantial loss of the investment. The method ofthe present invention provides a more reliable processing strategy withless risk than can be accomplished with conventional plating. Also,because the present invention allows for the plating of one wafer at atime, mistakes are less costly (e.g., conventional electroless platingprocesses operate on multiple wafers in parallel per plating tank step,so a deviation or defect in the process parameters in any givenstep/tank carries with it the attendant risk of damage to multiplewafers). However, multiple substrates may be plated in parallelaccording to the present invention. Thus, the present invention resultsin improved film quality, improved feature size capability, and a greatreduction of risk to finished substrates.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

Although the invention has been described in detail with particularreference to the preferred embodiments in the attachment, otherembodiments can achieve the same results. Variations and modificationsof the present invention will be obvious to those skilled in the art andit is intended to cover all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above, and of the corresponding application(s), arehereby incorporated by reference.

1. A plating apparatus comprising: a pressurized, sealable vessel; acontrollable plating fluid source linked to said vessel; a holdingapparatus to secure a substrate within said vessel during plating of thesubstrate and until the plating of the substrate is complete; and atleast one opening through which one or more plating fluids pass in andout of said vessel.
 2. The apparatus of claim 1 wherein the plating ofthe substrate comprises autocatalytic plating.
 3. The apparatus of claim1 wherein the substrate comprises a semiconductor wafer.
 4. Theapparatus of claim 1 wherein said linked controllable source and vesselcomprise a closed system.
 5. The apparatus of claim 1 further comprisinga pressure control system to control a pressure of said plating fluidwithin said vessel to control isostatic pressure.
 6. The apparatus ofclaim 1 wherein said controllable source comprises a system for thediscreet, sequential introduction and removal of said plating fluidsinto and from said vessel.
 7. The apparatus of claim 6 wherein saidsystem comprises a plurality of nozzles and conduits.
 8. The apparatusof claim 7 wherein said system comprises a sequentially rotating nozzlesystem.
 9. The apparatus of claim 1 further comprising a temperaturecontrol system.
 10. The apparatus of claim 9 wherein said temperaturecontrol system controls a temperature to within approximately ±1° C. 11.The apparatus of claim 9 wherein said temperature control system heatsor cools said plating fluid at a rate faster than approximately 0.5° C.per second.
 12. The apparatus of claim 11 wherein said temperaturecontrol system heats or cools said plating fluid at a rate faster thanapproximately 1.0° C. per second.
 13. The apparatus of claim 12 whereinsaid temperature control system heats or cools said plating fluid at arate faster than approximately 2.5° C. per second.
 14. The apparatus ofclaim 9 wherein said temperature control system is disposed outside ofsaid vessel to affect a temperature of said plating fluid prior to saidplating fluid entering said vessel.
 15. The apparatus of claim 9 whereinsaid temperature control system is disposed over said vessel.
 16. Theapparatus of claim 9 wherein said temperature control system is disposedin said vessel.
 17. The apparatus of claim 16 wherein said temperaturecontrol system is disposed in at least one wall of said vessel.
 18. Theapparatus of claim 1 wherein said vessel comprises a volume of less thanapproximately 5 liters.
 19. The apparatus of claim 18 wherein saidvessel comprises a volume of less than approximately 3 liters.
 20. Theapparatus of claim 19 wherein said vessel comprises a volume of lessthan approximately 2 liters.
 21. The apparatus of claim 20 wherein acell of said vessel comprises a volume of less than approximately 1liter.
 22. The apparatus of claim 21 wherein said vessel comprises avolume of less than approximately 0.5 liter.
 23. The apparatus of claim1 further comprising a baffle system disposed within said vessel. 24.The apparatus of claim 1 further comprising a cathode disposed in saidvessel.
 25. The apparatus of claim 1 wherein said vessel comprises: abase plate; and a cover removably disposed on said base plate.
 26. Theapparatus of claim 1 wherein said holding apparatus comprises a vacuumchuck.
 27. The apparatus of claim 26 wherein said vacuum chuckcomprises: a base; and at least one vacuum cavity in said base.
 28. Theapparatus of claim 27 further comprising at least one membrane disposedover said at least one cavity.
 29. The apparatus of claim 28 whereinsaid membrane comprises a membrane that is deformable in response to avacuum.
 30. The apparatus of claim 29 wherein said membrane comprises anelastomeric material.
 31. The apparatus of claim 27, said vacuum chuckfurther comprising a center shuttle disposed in said base.
 32. Theapparatus of claim 27 further comprising an edge seal boot disposed onsaid base.
 33. The apparatus of claim 32 wherein said edge seal bootcomprises an edge skirt to contact the substrate and seal a portion ofthe substrate.
 34. The apparatus of claim 33 further comprising anelectric bridge contact disposed in said edge skirt.
 35. The apparatusof claim 34 wherein said electric bridge contact comprises an array ofcontacts.
 36. A method for depositing metal on a substrate comprisingthe steps of: providing a pressurized, sealable vessel; securing thesubstrate within the vessel; introducing one or more plating fluids intothe vessel; removing the one or more plating fluids from the vessel; andremoving the substrate from the vessel after the metal has beendeposited on the substrate.
 37. The method of claim 36 furthercomprising; introducing the plating fluids discreetly and sequentially;and removing the plating fluids discreetly and sequentially.
 38. Themethod of claim 36 further comprising controlling an isostatic pressurewithin the vessel.
 39. The method of claim 36 further comprising thesteps of: disposing a cathode in the vessel; and sending an electricalcurrent to the cathode.
 40. The method of claim 36 further comprisingcontrolling a temperature of at least one of the plating fluids.
 41. Themethod of claim 40 comprising controlling the temperature to withinapproximately ±1° C.
 42. The method of claim 40 comprising heating orcooling at least one of the plating fluids at a rate faster thanapproximately 0.5° C. per second.
 43. The method of claim 42 comprisingheating or cooling at least one of the plating fluids at a rate fasterthan approximately 1.0° C. per second.
 44. The method of claim 43comprising heating or cooling at least one of the plating fluids at arate faster than approximately 2.5° C. per second.
 45. The method ofclaim 40 further comprising affecting the temperature of the at leastone fluid before introducing it into the vessel.
 46. The method of claim40 further comprising affecting the temperature of the at least onefluid inside the vessel.
 47. The method of claim 36 further comprisingthe steps of: providing a baffle system; and affecting the flow of theat least one fluid within the vessel using the baffle system.
 48. Themethod of claim 36 further comprising the steps of: providing a holdingapparatus; and disposing the holding apparatus in the vessel; andwherein the holding apparatus secures the substrate within the vessel.49. The method of claim 48 wherein the holding system comprises a vacuumchuck comprising at least one vacuum cavity.
 50. The method of claim 49further comprising the steps of: disposing a deformable membrane on theat least one cavity; and disposing the substrate on the membrane. 51.The method of claim 50 further comprising applying a vacuum to securethe substrate to the vacuum chuck.
 52. The method of claim 49 furthercomprising the steps of: providing a boot comprising an edge skirt; anddisposing the boot on the vacuum chuck.
 53. The method of claim 52further comprising the steps of: disposing an electrical bridge contactin the boot; and sending an electrical current through the bridgecontact.